In the field of gymnastic machines it is known to use at least one elongated member, usually an upright produced by extrusion, to carry an operating unit in a freely longitudinally slidable and selectively fixed manner. To fix this operating unit in a given operating position the use is well known of a regulating member, usually provided with a pin suitable to engage transversally the elongated member, for example in one hole of a plurality of holes obtained transversally in the upright. A blocking device is usually associated with the pin, and this latter presents an its own first end adequately shaped to engage stably one of the holes described above. Each pin presents, at opposite side from this first end, a head accessible by a user and usable to switch the position of the pin from the position of engagement of a hole of the upright to a release position, that allows to update the longitudinal position of the return unit along the upright. An example is shown in the patent document US20090170668 which discloses a gymnastic machine equipped with at least an operative unit provided with a handle and carried in slidable manner along a respective upright associated to the frame of the gymnastic machine itself. In particular, each operative unit of the machine according to document '668 is equipped with a respective blocking device suitable, in use, to selectively retain the position of the operative unit along the respective upright. In more details, the blocking device disclosed in the document '688 comprises a locking pin which, in use, is stably maintained by a spring in engagement of one of the holes made in the respective upright. In view of the above description, the regulating members provided with the blocking devices described above require the use of one hand to extract the pin from a corresponding hole of the upright and to maintain it separated from the upright to allow the longitudinal displacement of the unit, and the use of the other hand to perform at the same time this displacement.
It is clearly apparent that, in some low-automated sectors, wherein the operator must execute different and substantially contemporaneous tasks, the contemporaneous use of both the hands could be excessively onerous for the operator, at least due to the fact that the two tasks to be performed are complementary and intended for different activities. As shown above, with reference to patent document '668, the same problem exists also in the sector of the gymnastic machines, for example for adjusting the position of a seat or of a return member relative to the respective upright. In particular, taking into account the multi-station machines, wherein more users can train contemporaneously, occupying very near and sometimes shared spaces due to the particular conformation of these machines. In these cases, the users occupying contemporaneously spaces as those described above could hinder each other, and therefore the goal of optimising the exploitation of the space available in the gyms to maximise the hourly number of attendees could not be effectively achievable.
It is therefore appropriate to re-examine the way of using the return units associated with uprights in a slidable manner so as to change the conformation thereof in order to solve and possibly to overcome the drawbacks described above. It is clearly understood that this allows defining a new standard for the construction of return units and of machines provided with these return units, that are particularly practical to be used and, moreover, economical and safe.